Optically stimulated luminescence (OSL) and radio photoluminescence (RPL) are methods used for measuring doses from ionizing radiation. In typical arrangements, a device or material is optically stimulated and then emits luminescence (photons) as a result of the optical stimulation that is proportional to the ionizing radiation dose. Photons are detected using a sensitive light detector, such as a photomultiplier tube, and the signal from the detector is then used to calculate the dose that the material has absorbed.
Maximizing the signal-to-noise ratio (SNR) of the optical measurements is one of the main challenges in luminescence dosimetry. The major difficulty with achieving very high signal-to-noise ratios (SNR) at the extremely low ionizing radiation doses required for modern personnel dosimetry is the ability to minimize and ultimately reject background signals that are not related to the luminescence emission that is proportional to the ionizing radiation exposure.
As an example of the background noise problem, an OSL or RPL material, such as lithium fluoride (LiF) powder combined with a binder or polymer, introduces two sources of unwanted background luminescence that interferes with the measurement of the true OSL or RPL response and raises the minimum-detectable-dose (MDD) achievable with the composite dosimeter. During the optical stimulation process the optimal excitation light, blue light in the case of macro LiF, stimulates unwanted non-ionizing-radiation-dose-dependent emission light that partially overlaps the emission wavelengths of interest. Unwanted background fluorescence emanates from the LiF powder itself (both within the LiF crystal grain and also the surfaces of the LiF grains) and from the polymer. Optical bandpass filters placed adjacent to the light detector are selected to optimize the amount of good light emission reaching the light detector, while rejecting the majority of the out-of-band unwanted background light.
Despite very careful engineering of OSL reader systems, LiF polyethylene dosimeters (circa the late 2000s) still cannot measure much less than a few Gy due primarily with the fact that the sources of unwanted fluorescence overlap with the OSL emission band. What is needed is a new method of rejecting unwanted background fluorescence to achieve higher SNR in a composite material dosimeter.